Abstract

Myrmecophytic symbioses are widespread in tropical ecosystems and their diversity makes them useful tools for understanding the origin and evolution of mutualisms. Obligate ant–plants, or myrmecophytes, provide a nesting place, and, often, food to a limited number of plant–ant species. In exchange, plant–ants protect their host plants from herbivores, competitors and pathogens, and can provide them with nutrients. Although most studies to date have highlighted a similar global pattern of interactions in these systems, little is known about the temporal structuring and dynamics of most of these associations. In this study we focused on the association between the understory myrmecophyte Hirtella physophora (Chrysobalanaceae) and its obligate ant partner Allomerus decemarticulatus (Myrmicinae). An examination of the life histories and growth rates of both partners demonstrated that this plant species has a much longer lifespan (up to about 350 years) than its associated ant colonies (up to about 21 years). The size of the ant colonies and their reproductive success were strongly limited by the available nesting space provided by the host plants. Moreover, the resident ants positively affected the vegetative growth of their host plant, but had a negative effect on its reproduction by reducing the number of flowers and fruits by more than 50%. Altogether our results are important to understanding the evolutionary dynamics of ant–plant symbioses. The highly specialized interaction between long-lived plants and ants with a shorter lifespan produces an asymmetry in the evolutionary rates of the interaction which, in return, can affect the degree to which the interests of the two partners converge.

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Acknowledgments

We are grateful to T. Goslar from the Poznan Radiocarbon Laboratory, Poland and M. Paterne from the LSCE CNRS-CEA, France, for their help in the determination of the 14C age, to C. Trontin for her valuable assistance in the lab and to Andrea Dejean for proofreading the manuscript. We would like to thank V. Rico-Gray and two anonymous reviewers for their valuable comments on the manuscript. We would also like to thank the Laboratoire Environnement de Petit Saut for furnishing logistical assistance. Financial support for this study was provided by the Programme Amazonie II (project 2ID) of the French Centre National de la Recherche Scientifique (CNRS), by the Programme Convergence 2007–2013 Région Guyane (project DEGA) from the European Community, by a research program of the French Agence Nationale de la Recherche (research agreement no. ANR-06-JCJC-0109-01), and by the ESF-EUROCORES/TECT/BIOCONTRACT program. The experiments comply with the current laws of France.